KR20120120073A

KR20120120073A - Improved polycrystalline texturing composition and method

Info

Publication number: KR20120120073A
Application number: KR1020120041594A
Authority: KR
Inventors: 로버트 케이. 바; 코리 오'코너
Original assignee: 롬 앤드 하스 일렉트로닉 머트어리얼즈, 엘.엘.씨.
Priority date: 2011-04-21
Filing date: 2012-04-20
Publication date: 2012-11-01

Abstract

PURPOSE: An improved polycrystalline texturing composition and method are provided to provide isotropic etch and to reduce incident light reflectance. CONSTITUTION: An improved polycrystalline texturing composition comprises one or more alkali compounds, one or more fluorine ion supply source, and one or more oxidant supply source, and pH is 7 or less. A manufacturing method of poly-crystal texturing method comprises: a step of providing a polycrystalline semiconductor wafer; step of isotropically etching a non-doped semiconductor wafer by contacting crystalline semiconductor wafer with a composition which comprises one or more alkali compound, one or more fluorine ion source, one or more oxidants and has pH of 7 or less.

Description

Improved polycrystalline texturing composition and method

The present invention relates to improved acidic polycrystalline semiconductor texturing compositions and methods. More specifically, the present invention aims at improved acidic polycrystalline semiconductor texturing compositions and methods that provide isotropic etch and reduce incident light reflectance.

Polycrystalline semiconductor wafers are typically made of silicon or other similar ceramic materials and have a grain size that varies from thousands of angstroms to 2-3 μm. Such wafers can be used in the manufacture of photovoltaic devices. A solar cell is a device that converts light energy incident on a surface, such as sunlight, into electrical energy. Polycrystalline silicon semiconductor wafers are formed by a chemical vapor deposition process, in which silane is decomposed at elevated temperatures to form ingots or similar types of articles. Are manufactured. Ingots are cut with appropriate cutting saws and cutting methods used in industry and inserted into wafers of various sizes and shapes. Saw damage to the surface of the wafer can increase the reflectivity of the wafer by more than 35%. High reflectance reduces the incident light absorption capability of the wafer and degrades the performance of the solar cell in which the wafer is used. Various attempts have been made to increase the absorption of light by lowering the reflectance of incident light on the surface of solar cells. When the reflectance of the incident light is lowered, the conversion efficiency of light into electrical energy increases. Typically, texturing is performed on the semiconductor surface to reduce the incident light reflectance.

Texturing is frequently done with alkaline materials such as sodium hydroxide or potassium hydroxide, but these alkaline texturing materials act too anisotropically to be efficient texturizers. In addition, alkali metal hydroxides tend to leave undesired crusts or residues on the wafer that are difficult to remove. Tetramethylammonium hydroxide etching is less anisotropic than alkali metal hydroxides, but still exposes grain boundaries too easily. Some crystalline orientation etch is faster than other anisotropic etch and the grain boundaries are exposed to recombination sites and degrade solar cell efficiency. In general, recombination is a process in which mobile electrons and electron holes are removed and energy is lost in a form that cannot be used by solar cells.

Another problem caused by exposure of grain boundaries is reduced shunt resistance, R _SH . Low shunt resistance causes power losses in the solar cell by providing a different current path for the current generated by light. This diversion reduces the amount of current flowing through the solar cell junction and the voltage from the solar cell. The effect of shunt resistance is particularly severe at low light levels, since there is less light-generated current. Therefore, current losses to these shunts have a serious impact on battery performance.

Although acid etching, such as hydrofluoric acid and nitric acid mixtures, provides acceptable isotropic etching for silicon polycrystalline semiconductor wafers, this presents several problems. These substances are not only dangerous, but require extreme care in their operation, storage, use and disposal. Depending on local and regional disposal practices, the disposal of these materials may be costly. Texturing a polycrystalline wafer with a hydrofluoric acid and nitric acid mixture includes diluting concentrated 49% hydrofluoric acid and 69% nitric acid to produce a bath comprising 10% hydrofluoric acid and 35% nitric acid. This is an exothermic reaction that can harm the operator of the acid. In addition, a running bath of the acid mixture contains a large amount of acid waste, which is quite expensive to replenish, manufacture of a large amount of acid and produce waste that is harmful to the environment. Generally, polycrystalline silicon semiconductor wafers treated with hydrofluoric acid and nitric acid mixtures having an average reflectance of 27% at light wavelengths of 400 nm to 1100 nm are currently accepted in the industry; The lower the reflectance, the better the efficiency of the solar cell. The current industry goal is to achieve a reflectance of less than 20% at light wavelengths of 400 nm to 1100 nm. Accordingly, there is a need for improved isotropic texturing compositions and methods to improve solar cell performance.

In one aspect, the composition comprises at least one alkali compound, at least one source of fluorine ions, at least one source of oxidant and has a pH of less than 7.

In another aspect, a method includes providing a polycrystalline semiconductor wafer; And isotropically etching the non-doped semiconductor wafer by contacting the polycrystalline semiconductor wafer with a composition comprising at least one alkali compound, at least one source of fluorine ions, at least one oxidant and having a pH of less than 7. It includes.

The acidic compositions and methods texture the polycrystalline semiconductor wafers isotropically, reducing or preventing recombination and shunting. Incident light reflectance is also reduced compared to conventional acidic and alkali texturing compositions and methods. Thus, the polycrystalline semiconductor wafer textured with the composition and the balance thereof improves solar cell efficiency and performance. Furthermore, the manipulation, use and storage of the acidic composition is not harmful to the operator or the environment to the same extent as conventional hydrofluoric acid and nitric acid anisotropic texturing solutions. Furthermore, the costs for its manufacture, maintenance and waste disposal are low compared to conventional hydrofluoric acid and nitric acid anisotropic texturing solutions.

As used throughout this specification, the terms "composition" and "solution" are used interchangeably. The term "isotropic" means unchanged with respect to direction. The term "anisotropy" means a property that changes in direction. As used throughout this specification, the following abbreviations have the following meanings unless the context indicates otherwise: ° C = degrees Celsius; A = amps; dm = decimeter; Μm = micron; nm = nanometer; SEM = scanning electron micrograph; UV = ultraviolet; And IR = infrared. Unless otherwise indicated, all percentages and ratios are by weight. All numerical ranges include those ranges, and can be combined in any order, except where it is logical to interpret these numerical ranges as adding up to 100%.

The composition comprises at least one ammonia derivative, at least one source of fluorine ions, at least one oxidant and has a pH of less than 7. The composition is an aqueous acidic solution. The composition is substantially free of alkali metal hydroxides. The acidic composition isotropically textured the polycrystalline semiconductor wafer without substantially exposing the grain boundaries, thereby reducing or preventing recombination and shunting. In addition, incident light reflectance is reduced compared to many conventional acidic and alkali texturing compositions and methods. On average, the light reflectance at light wavelengths of 400 nm to 110 nm is 22% or less. In addition, the adhesion of the metal to the surface of the wafer is improved. Thus, the polycrystalline semiconductor wafers textured with the compositions and methods improve the efficiency and performance of solar cells. Furthermore, the manipulation, use and storage of the acidic composition is not harmful to the operator or the environment to the same extent as conventional hydrofluoric acid and nitric acid anisotropic texturing solutions. Furthermore, the costs for its manufacture, maintenance and waste disposal are low compared to conventional hydrofluoric acid and nitric acid anisotropic texturing solutions.

At least one alkali compound that isotropically texturizes the polycrystalline semiconductor wafer is included in the texturing composition. Such alkaline compounds include, but are not limited to, amines such as alkanolamines and quaternary ammonium compounds. Such compounds are included in amounts of 1% to 20%, such as 1% to 10% or 1% to 5% of the texturing composition. Alkanolamines include, but are not limited to, compounds having the following general formula:

R ₃ _- _n N (C _m H _2m (OH)) _n

Wherein R is a hydrogen atom or an alkyl group having 1 to 4 carbons, m is an integer from 2 to 4 and n is an integer from 1 to 3. Examples of such compounds are monoethanolamine, diethanolamine, triethanolamine, propanolamine, dipropanolamine, tripropanolamine, isopropanolamine, diisopropanolamine, triisopropanolamine, butanolamine, N-methylethanolamine, N-methyl Diethanolamine, N, N-dimethylaminoethanol, N-ethylethanolamine, N-ethyldiethanolamine, N, N-diethanolamine, N, N-butylethanolamine, N, N-dibutylethanolamine and Its salts. Preferred alkanolamines are monoethanolamine, diethanolamine and triethanolamine.

Quaternary ammonium compounds include, but are not limited to, compounds having the following general formula:

OH ^-

Wherein R ₁ to R ₄ independently of one another are hydrogen, (C ₁ -C ₆ ) alkyl group, (C ₁ -C ₆ ) hydroxyalkyl group, (C ₆ -C ₁₀ ) aryl group or (C _7- C ₁₁ ) alkylaryl group. Examples of such compounds are ammonium hydroxide, tetramethyl ammonium hydroxide (TMAH), tetraethyl ammonium hydroxide, tetrapropyl ammonium hydroxide, tetrabutyl ammonium hydroxide, tetramethyl-2-hydroxyethyl ammonium hydroxide (choline), trimethyl-3 hydroxide -Hydroxypropyl ammonium, trimethyl-3-hydroxybutyl ammonium hydroxide, trimethyl-4-hydroxybutyl ammonium hydroxide, triethyl-2-hydroxyethyl ammonium hydroxide, tripropyl-2-hydroxyethyl ammonium hydroxide, trihydroxide Butyl-2-hydroxyethyl ammonium hydroxide, dimethylethyl-2-hydroxyethyl ammonium hydroxide, dimethyldi (2-hydroxyethyl) ammonium hydroxide, monomethyltri (2-hydroxyethyl) ammonium hydroxide, monomethyltripropyl hydroxide Ammonium Hydroxide, Monomethyltributyl Ammonium Hydroxide, Monoethyltrimethyl Ammonium Hydroxide, Monoethyltributyl Ammonium Hydroxide Dimethyldiethyl ammonium hydroxide, dimethyldibutyl ammonium hydroxide, benzyl trimethylammonium hydroxide, benzyl triethylammonium hydroxide, benzyl tributylammonium hydroxide, phenyltrimethylammonium hydroxide and phenyl triethylammonium hydroxide. Preferably, the quaternary ammonium compound is selected from ammonium hydroxide, tetramethylammonium hydroxide, tetramethyl-2-hydroxyethyl ammonium hydroxide and benzyl trimethylammonium hydroxide.

One or more sources of fluorine ions are included in the composition. The fluorine ion source is isotropically textured and provides an acidic environment. Fluorine ion sources include, but are not limited to, bifluoride and fluoride salts. Bifluoride salts include, but are not limited to, sodium bifluoride and alkali metal bifluoride salts such as potassium bifluoride, ammonium bifluoride, tin bifluoride and antimony bifluoride. Preferably, the bifluorinated compound is included in the composition. Fluorine ion sources are included in amounts of 1% to 40%, such as 5% to 15%.

One or more oxidants are included in the composition. Such oxidants include, but are not limited to, hydrogen peroxide and salts thereof, hypochlorite, persulfate, peroxyorganic acid, permanganate salt, sodium hypochlorite, sodium percarbonate (sodium percarbonate), chlorate, nitric acid and salts thereof, periodate, perbromate, periomate, iodate, perchlorate and bromate do. Such oxidants are included in amounts of 0.05% to 5%, such as 0.5% to 1%.

Optionally, the aqueous acidic composition may comprise one or more surfactants. Surfactants include nonionic, anionic, cationic and amphoteric surfactants. Conventional surfactants may be used. Such surfactants are generally commercially available. Typically, the surfactant is a low foam surfactant. If surfactants are included in the composition, they are included in amounts of 0.5% to 10%.

The components included in the aqueous acidic texturing composition may be added in any order. They can be mixed together and then dissolved in a sufficient amount of water. Alternatively, they can be added to a sufficient amount of water at one time. Heating may be necessary to help dissolve the components.

The aqueous acidic texturing composition has a pH of less than 7, such as less than 6 or less than 3-5 or less than 4-5. Typically, texturing is done on both sides of the wafer. Typically, the wafer is bulk-doped prior to texturing. Typically, bulk-doping is done with boron, but polycrystalline wafers may be bulk-doped with other materials well known in the art. The acidic texturing composition can be applied to the polycrystalline semiconductor wafer by any suitable method known in the art. The polycrystalline semiconductor wafer may be immersed in the texturing composition, the composition may be sprayed onto the polycrystalline semiconductor wafer, or the composition may be used in conventional ultrasonic cleaning processes. The texturing composition may be applied at room temperature to 90 ° C., typically at 50 ° C. to 80 ° C. The texturing composition is applied to the surface of the polycrystalline semiconductor wafer for a dwell time of 5 to 40 minutes, typically 10 to 30 minutes. The polycrystalline semiconductor wafer is then optionally rinsed with water. After the polycrystalline semiconductor wafer is textured, it is processed using conventional residual amounts of photovoltaic devices such as solar cells.

The reflectance of incident light by the textured polycrystalline semiconductor wafer is 22% or less, typically 20% or less, more typically 15% to 20%, at an incident light wavelength of 400 nm to 1100 nm. Polycrystalline semiconductors textured with an acidic aqueous composition can be used in devices that convert incident light into electrical energy, such as sunlight, lasers, fluorescence derived light, as well as other sources of light. Such devices include, but are not limited to, solar cells, photo and electrochemical detectors / sensors, biodetectors / biosensors, catalysts, electrodes, gate electrodes, ohmic contacts, interconnect lines. Schottky barrier diode contacts and optoelectronic components.

After the polycrystalline semiconductor wafer is textured, it is further doped to provide a PN junction when bulk-doped. If the polycrystalline wafer is not bulk-doped, it is bulk-doped or p-doped, such as boron, and then further doped to provide a PN junction. The production or ion implantation of the semiconductor PN junction phosphorus diffusion occurs at the front of the wafer to produce n-doped (n + or N ++) regions. The n-doped region may be considered an emitter layer.

In the fabrication of photovoltaic devices or solar cells, the entire back side of a polycrystalline semiconductor wafer may be metal coated or only a portion of the back side may be metal coated, such as to form a grid. Such backside metallization may be accomplished by a variety of techniques and may be performed prior to metallization of the wafer front side. In one embodiment, the metal coating was applied in the form of a silver-containing paste, an aluminum-containing paste or an electrically conductive paste such as silver and aluminum-containing paste; Other suitable pastes known in the art may also be used. Typically such conductive pastes comprise conductive particles embedded in a glass matrix and organic binder. The conductive paste may be applied to the wafer by various techniques such as screen printing. After the paste is applied, it is heated to remove the organic binder. If a conductive paste containing aluminum is used, the aluminum may be partially diffused on the backside of the wafer, or alloyed with silver when used in the form of a paste that also contains silver. Optionally, a seed layer can be deposited on the backside of the polycrystalline semiconductor wafer and a metal coating can be deposited into the seed layer by electroless or electrolytic plating.

An anti-reflective layer may be added to the front side or emitter layer of the wafer. The antireflection layer may also function as a passivation layer. Suitable antireflective layers include, but are not limited to, silicon oxide layers such as SiO ₂ , silicon nitride layers such as Si ₃ N ₄ , combinations of silicon oxides and silicon nitride layers, and silicon oxide layers having titanium oxides such as TiO _x , silicon Combinations of nitride layers. In the preceding formulae, x is an integer representing the number of oxygen atoms. Such antireflection layers may be deposited by various vapor deposition methods, for example, chemical vapor deposition and physical vapor deposition.

The front surface of the polycrystalline semiconductor wafer includes a metallized pattern. For example, the front surface of the wafer may consist of a current collecting line and a current busbar. Current collection lines typically traverse the busbar and have a relatively fine structure (ie dimensions) compared to current busbars.

The pattern can pass through the antireflective layer to expose the semiconductor body surface of the wafer. Alternatively, trenches may be formed in the openings to form selective emitters. These trenches may be high doping regions. Various processes may be used to form the pattern, including, but not limited to, laser ablation, mechanical means, and lithography processes, all of which are well known in the art. Such mechanical means include sawing and scratching. Typical lithography processes include lamination of imageable material on the surface of the wafer, patterning of the imageable material to form openings in the antireflective layer, transferring the pattern to the wafer, lamination of nickel layers in the openings, and Removal of the imageable material. In one embodiment, the imageable material has been removed prior to the step of depositing a metal layer in the opening. In another embodiment, the imageable material has been removed after depositing a metal layer in the opening. If an imageable material is present in the metal deposition step, typically this imageable material avoids any dyes, such as contrast dyes absorbed at the wavelength of radiation used during the nickel deposition step ( avoid). Imagingable materials present during the plating step typically include dyes having a minimum light transmittance of 40% to 60%.

The imageable material can be removed with any suitable polymer remover. Such removers may be alkali, acidic or essentially neutral and are well known in the art.

The front side of the wafer may be metallized using a conductive paste, which may be the same as or different from any conductive paste used on the back side of the wafer. Any conductive paste used to metallize the front side of the wafer typically does not contain aluminum. The temperature used for firing the paste depends on the thickness of all the antireflective layers used, the particular paste used, among other factors. Such temperatures may be appropriately selected by those skilled in the art. It is also understood by those skilled in the art that the heat treatment process can be performed in an oxygen-containing atmosphere, an inert atmosphere, a reducing atmosphere, or a combination thereof. For example, the heat treatment may be carried out at a first temperature under an atmosphere of little oxygen and then at a second temperature under an inert atmosphere or a reducing atmosphere, where the second temperature is higher than the first temperature.

After the heat treatment process, the wafer may optionally be contacted with a buffered acidic solution, such as a buffered hydrofluoric acid solution, to remove all oxides generated during the heat treatment. Such contact may also be done by spraying a solution onto the wafer, immersing the wafer in such a solution, or by other suitable means.

After the front side pattern and back side of the wafer are metallized using the conductive paste, the metal layer is laminated to the conductive pattern on the front side. This metal layer may be any suitable conductive metal such as gold, silver or copper, and is typically silver. Such metals may be deposited by methods known in the art. In one embodiment, the laminated metal layer was composed of the same metal used in the conductive paste. For example, silver layers have been laminated to silver-containing conductive pastes.

Silver may be deposited by light induced plating (LIP) or conventional silver electroplating methods well known in the art. If LIP is used, the backside of the semiconductor wafer is connected to an external current source (rectifier). A silver anode located in the silver plating composition is connected to the rectifier to form a completed circuit between the elements. Typical current density is 0.1 A / dm ² To 5 A / dm ² . The total current requirement depends on the specific size of the wafer used. The silver anode also provides an easy source of silver ions that replenishes silver ions in the silver plating composition without the use of an external source. The light source is positioned to illuminate the semiconductor wafer with light energy. The light source can be, for example, a fluorescent or LED lamp that provides energy within a wavelength at which the semiconductor wafer is photovoltaically sensitive. Various other light sources can be used, non-limiting examples. Incandescent lamps such as 75 watt and 250 watt lamps, mercury lamps, halogen lamps and 150 watt IR lamps. Examples of commercially available silver plating compositions are ENLIGHT ™ Silver Plate 600 and 620 from Rohm and Haas Electronic Materials, LLC, Marlborough, Massachusetts.

The plating cell is a chemically inert material with respect to the plating composition and has a minimum light transmittance of 40-60%. In addition, the wafer may be positioned horizontally in the plating cell and illuminated from above the silver plating composition, in which case the plating cell need not have at least a minimum light transmittance.

In another embodiment, a metal seed layer can be laminated to the front conductive pattern instead of the metal paste. Typically the metal seed layer is nickel. The nickel seed layer may be deposited by any conventional nickel lamination method known in the art. Typically, the nickel seed layer is deposited by light assisted nickel deposition. If the source of nickel is an electroless nickel composition, plating is performed without the application of an external current. If the source of nickel is an electrolytic nickel composition, the backside potential (rectifier) is applied to the semiconductor wafer plate. The light can be continuous or pulsed. Typically, prior to the deposition of nickel, the surface oxides are removed from the conductive pattern using 1% hydrofluoric acid solution.

Light that can be used in the plating process is, but is not limited to, visible light, IR, UV, and X-rays. Light sources include, but are not limited to, incandescent lamps, LED lights (photo-emitting diodes), infrared lamps, fluorescent lamps, halogen lamps, and lasers.

Typically, nickel is deposited through openings in the antireflective layer and deposited onto the exposed, textured surface of the polycrystalline semiconductor wafer using an electroless nickel plating composition. Examples of commercially available electroless nickel compositions include DURAPOSIT ™ SMT 88 Electroless Nickel and NIPOSIT ™ PM 980 and PM 988 Electroless Nickel. All of these are products from Rohm and Haas Electronic Materials, LLC, Marlborough, Massachusetts.

Electrolytic nickel compositions may also be used. When an electrolytic composition is used, not only light but also applied backside potential (rectifier) is used to deposit nickel. Typical current densities are from 0.1 A / dm ² to 2 A / dm ² . The specific current demand depends on the specific size of the wafer used. The electroplating process used is conventional. Suitable electrolytic nickel plating baths are commercially available and have been described in many literatures. An example of a commercially available electrolytic nickel bath is Rohm & Haas NICKEL GLEAM ™ Electrolytic Nickel.

By illuminating the front surface of the polycrystalline semiconductor wafer with light energy, plating takes place on the front surface. Impinging light energy creates a current in the semiconductor. The plating rate of the front surface can be controlled by adjusting the intensity of light, the temperature of the bath, the activity of the reducing agent, the initial wafer conditions, the doping level, as well as other parameters known to those skilled in the art. When the plating bath is an electrolytic bath, the plating rate can also be adjusted by the rectifier. Typically a 20 nm to 300 nm thick nickel layer, with the correct thickness depending on the application, size, pattern, and geometry, is preferred.

After nickel is deposited through the opening and adjacent to the exposed surface of the polycrystalline semiconductor wafer substrate, silver is deposited adjacent to the nickel. Conventional electroplating silver compositions can be used. The silver composition may be cyanide or silver composition free of cyanide containing the silver composition.

Silver may be deposited on nickel by light induction plating (LIP) or conventional silver electroplating methods known in the art. The LIP plating process is similar to plating the silver paste. Preference is given to silver layers having a thickness of 1 μm to 30 μm, which have the correct thickness depending on various factors such as application, size, pattern and geometry.

After the silver metal is deposited on and around the nickel, the semiconductor is sintered to form nickel silicide. Sintering is performed on the silver deposited on the nickel surface to improve the adhesion between silver and nickel. Improved bonding between nickel and silicon reduces the likelihood of adhesion failure between nickel silicide and silver. In addition, since silver is not bonded to the silicide by the sintering temperature, nickel silicide is formed with silver which prevents oxidation of nickel during sintering. Furnaces that provide a wafer peak temperature of 380 ° C. to 550 ° C. may be used. Typically the maximum temperature time ranges from 2 seconds to 20 seconds. An example of a suitable furnace is a lamp furnace (IR).

Since the silver layer prevents the oxidation of nickel during sintering, the sintering can be done not only in an inert gas atmosphere or vacuum but also in an oxygen containing environment. Generally, sintering is performed for 3 to 10 minutes. The line speed at which the semiconductor passes through the furnace depends on the furnace used. Secondary experiments may be conducted to determine the appropriate line speed. Typically, the line speed is between 330 cm / min and 430 cm.

After the polycrystalline semiconductor wafer is metallized, additional conventional steps may be performed on the metallized semiconductor to complete the photovoltaic device formation. Such methods are well known in the art.

The following examples are intended to illustrate the invention in more detail, and do not limit the scope of the invention.

Textured polycrystalline semiconductors have a reduced incident light reflectance.

1 is a 5000 × SEM of a silicon polycrystalline bulk-doped semiconductor wafer, textured with a 10% hydrofluoric acid and 50% nitric acid mixture;
FIG. 2 is a 5000 × SEM of a silicon polycrystalline bulk-doped semiconductor wafer textured with a 7.5% TMAH, 1% hydrogen peroxide and 15% ammonium bifluoride mixture;
3 is a 2500 × SEM of a silicon polycrystalline bulk-doped semiconductor wafer textured with 9% TMAH aqueous solution.

Example 1

An isotropic aqueous texturing composition containing 10% hydrofluoric acid and 50% nitric acid was prepared. The pH of the acid mixed texturing solution is less than one. The weight of the bulk-doped polycrystalline silicon wafer 125 mm ² was measured and recorded using a conventional analytical balance. The wafer was then immersed in an isotropic aqueous texturing solution at 10 ° C. for 3 minutes. The wafer was removed from the solution, rinsed with deionized water for 1 minute, dried at room temperature and weighed. The amount of etching on both sides of the wafer was 4.5 탆 as calculated using a conventional method from weight loss during texturing, area of the wafer, and density of silicon. 1 is a 5000 × SEM of a textured wafer. No exposed grain boundary was observed.

The reflection of the wafer was then measured using a MacBeth ColorEye ™ Reflectometer. The reflectance was recorded in 10 nm units in the wavelength range of 1100 nm to 400 nm. Average% reflectance was calculated with a reflectometer for this range. The average incident light reflectance was determined to be 25.44%, which is higher than the desired reflectance of less than 20%.

Example 2

The following isotropic aqueous acidic texturing solution was prepared.

ingredient Content-weight percent Tetramethylammonium Hydroxide 7.5% Hydrogen peroxide One% Ammonium Bifluoride 15% water Balance

The weight of the bulk-doped polycrystalline silicon wafer was measured and recorded. Thereafter, it was soaked in the solution for 10 minutes at 80 ° C. The pH of the solution was 4. The wafer was then removed from the solution, rinsed with deionized water and dried in air. As a result of measuring the weight of the wafer, the amount of silicon etched from both sides of the wafer was determined to be 4.73 mu m. 2 shows the surface of a textured wafer. No exposed grain boundary was observed.

The reflectance of the wafer was measured using a MacBeth ColorEye ™ Reflectometer. The reflectance was recorded in 10 nm units in the wavelength range of 1100 nm to 400 nm. Average% reflectance was calculated by reflectometer for this range. The average incident light reflectance was determined to be 15.37%. Texturing with the compositions disclosed in Table 1 above provides a polycrystalline wafer that exhibits reduced incident light reflectance in contrast to the case of the acid mixed formulation of Example 1.

Example 3

The following isotropic aqueous acidic texturing solution was prepared.

ingredient Content-weight percent Tetramethylammonium Hydroxide 5.25% Hydrogen peroxide 0.7% Ammonium Bifluoride 10.25% water Balance

The weight of the bulk-doped polycrystalline silicon wafer was measured and recorded. Thereafter, it was soaked in the solution at 85 ° C for 12 minutes. The pH of the solution was 4. The wafer was then removed from the solution, rinsed with deionized water and dried in air. As a result of measuring the weight of the wafer, the amount of silicon etched from both sides of the wafer was determined to be 4.42 mu m. The surface of the etched silicon wafer had a similar appearance to that of FIG. In addition, no exposed grain boundaries were observed.

The reflectance of the wafer was measured using a MacBeth ColorEye ™ Reflectometer. The reflectance was recorded in 10 nm units in the wavelength range of 1100 nm to 400 nm. Average% reflectance was calculated by reflectometer for this range. The average incident light reflectance was determined to be 17.68%. Texturing with the compositions disclosed in Table 2 above provides a polycrystalline wafer exhibiting a reduced incident light reflectance as opposed to the case of the acid mixed formulation of Example 1.

Example 4

The following isotropic aqueous acidic texturing solution was prepared.

ingredient Content-weight% Ammonium hydroxide 2.89% Hydrogen peroxide One% Ammonium Bifluoride 15% water Balance

The weight of the bulk-doped polycrystalline silicon wafer was measured and recorded. Thereafter, it was soaked in the solution for 10 minutes at 80 ° C. The pH of the solution was 4. The wafer was then removed from the solution, rinsed with deionized water and dried in air. As a result of measuring the weight of the wafer, the amount of silicon etched from both sides of the wafer was determined to be 4.26 mu m. The surface of the etched silicon wafer had a similar appearance to that of FIG. In addition, no exposed grain boundaries were observed.

The reflectance of the wafer was measured using a MacBeth ColorEye ™ Reflectometer. The reflectance was recorded in 10 nm units in the wavelength range of 1100 nm to 400 nm. Average% reflectance was calculated by reflectometer for this range. The average incident light reflectance was determined to be 18.11%. Texturing with the compositions disclosed in Table 3 above provides a polycrystalline wafer that exhibits reduced incident light reflectance in contrast to the case of the acid mixed formulation of Example 1.

Example 5

The following isotropic aqueous acidic texturing solution was prepared.

ingredient Content-weight percent Monoethanolamine 10% Hydrogen peroxide One% Ammonium Bifluoride 20% water Balance

The weight of the bulk-doped polycrystalline silicon wafer was measured and recorded. Thereafter, it was immersed in the solution for 10 minutes at 60 ℃. The pH of the solution was 4. The wafer was then removed from the solution, rinsed with deionized water and dried in air. As a result of measuring the weight of the wafer, the amount of silicon etched from both sides of the wafer was determined to be 2.61 mu m. The surface of the etched silicon wafer had a similar appearance to that of FIG. In addition, no exposed grain boundaries were observed.

The reflectance of the wafer was measured using a MacBeth ColorEye ™ Reflectometer. The reflectance was recorded in 10 nm units in the wavelength range of 1100 nm to 400 nm. Average% reflectance was calculated by reflectometer for this range. The average incident light reflectance was determined to be 19.82%. Texturing with the compositions disclosed in Table 4 above provides a polycrystalline wafer that exhibits reduced incident light reflectance as opposed to the case of the acid mixed formulation of Example 1.

Example 6

An anisotropic aqueous alkali texturing solution consisting of 9% tetramethylammonium hydroxide was prepared. The pH of the texturing solution is at least 13. Bulk-doped polycrystalline silicon wafers were measured and recorded using conventional analytical balances. The wafer was then immersed in an anisotropic texturing solution at 70 ° C. for 5 minutes. The wafer was removed from the solution, rinsed with deionized water for 1 minute, dried at room temperature and weighed. The amount of etching on both sides of the wafer was calculated to be 4.38 mu m. The foreground of the SEM shows the pyramid structure formed by alkali TMAH texturing. In the region behind the pyramid structure, grain boundaries were undesirably exposed by the TMAH alkaline solution. This grain boundary is not observed in the isotropic texturing of Example 1-5.

The reflection of the wafer was then measured using a MacBeth ColorEye ™ Reflectometer. The reflectance was recorded in 10 nm units in the wavelength range of 1100 nm to 400 nm. Average% reflectance was calculated with a reflectometer for this range. The average incident light reflectance was determined to be 27.10%, which is much larger than the isotropic texturing solution of Example 2-5 having an average incident light reflectance value of Example 1-5, in particular an average incident light reflectance value below 20%.

Claims

A composition comprising at least one alkali compound, at least one source of fluorine ions, at least one source of oxidant and having a pH of less than 7.

The composition of claim 1, wherein the at least one alkaline compound is selected from alkanolamines and quaternary ammonium compounds.

The composition of claim 2 wherein the alkanolamine has the general formula:
R ₃ _- _n N (C _m H _2m (OH)) _n
Wherein R is a hydrogen atom or an alkyl group having 1 to 4 carbons, m is an integer from 2 to 4 and n is an integer from 1 to 3.

The composition of claim 2 wherein the quaternary ammonium compound has the general formula:
OH ^-

Wherein R ₁ to R ₄ independently of one another are hydrogen, (C ₁ -C ₆ ) alkyl group, (C ₁ -C ₆ ) hydroxyalkyl group, (C ₆ -C ₁₀ ) aryl group or (C _7- C ₁₁ ) alkylaryl group.

The composition of claim 1, wherein the at least one fluorine ion is selected from bifluorinated and fluorinated salts.

The method of claim 1, wherein the one or more oxidizing agents are hydrogen peroxide and salts thereof, hypochlorite, persulfate, peroxyorganic acid, permanganate salt, sodium hypochlorite, peroxide From sodium carbonate, chlorate, nitric acid and salts thereof, periodate, perbromate, iodide, iodate, perchlorate and bromate Composition selected.

The composition of claim 1 wherein the pH is 3-5.

a) providing a polycrystalline semiconductor wafer; And
b) isotropically etching the non-doped semiconductor wafer by contacting the polycrystalline semiconductor wafer with a composition comprising at least one alkali compound, at least one source of fluorine ions, at least one oxidant and having a pH of less than 7. Method comprising the steps.

A polycrystalline semiconductor wafer processed according to the method of claim 8, having an incident light reflectance of 22% or less at an incident light wavelength of 400 nm to 1100 nm.

The polycrystalline semiconductor wafer according to claim 9, wherein the incident light reflectance is 20% or less at an incident light wavelength of 400 nm to 1100 nm.

10. The polycrystalline semiconductor wafer of claim 9 free of grain boundaries substantially exposed to the surface.